1. Field of the Invention
This invention relates to a device for positioning glass sheets advancing flat on a conveyor and, particularly, glass sheets heated beyond their softening temperature, in preparation for their bending. It applies, for example, to the production of automobile glazings.
2. Discussion of the Related Art
A correct positioning, or more precisely a correct orientation, of glass sheets on a horizontal conveyor is systematically necessary since the latter must occupy a predetermined position in a treatment station. Ordinarily, to bring the glass sheets to the desired position, alignment devices are used which act on the edges of the glass sheets with the help of spindles or pins.
The alignment of the glazings is not very difficult when these glazings are at ambient temperature, which is the case, for example, during the cutting or polishing of the edges. But when these glazings are heated beyond the softening temperature, for example immediately before a bending station or inside it, the pins or spindles acting on their edges cause local deformations which harm the optical properties of the glazing. It is possible to avoid any alignment in the longitudinal direction of the conveyor by determining with an edge detector operating without contact, for example one of the photoelectric barrier type, the moment when the edge of a glass sheet passes a given point selected on the conveying path and by calculating on the basis of this time signal the moment when, considering the speed of the conveyor, the glazing will reach its final position in the longitudinal direction and therefore when the rollers of the conveyor will have to be immobilized. However, the positioning of the glass sheets in relation to the crosswise direction of the conveyor cannot be avoided and for this purpose it is necessary to displace them with push pins or rods which act on their edges.
A positioning device is known from U.S. Pat. No, 3,701,643, comprising a carriage which is positioned laterally beside the horizontal conveyor, and moved parallel to it and in synchronism with the glass sheet. On this carriage is mounted at least one thrust rod which is mobile to a predefined extent, advancing transverse to the direction of displacement of the carriage, and acting on a lateral edge of the glass sheet. According to said document, the thrust rods are actuated by pneumatic cylinders whose piston rods have paths limited at both stroke ends by stops, of which the front stop is mounted in a place corresponding to the desired position of the glazing.
With this known positioning device, the action of the thrust rods on the lateral edges of the glass sheets is an intermittent or jerking action. Therefore, there is a danger that the softened glass sheet will be locally deformed by the contact with jerking.